A new I-131 labeled antibody is being tested. This antibody, CC-49 recognizes TAG-72 the same antigen recognized by B72.3. We have imaged 3 patients with lung carcinoma. The biodistribution is similar to that of I-131 B72.3. At present the number of patients is small to make comparisons between CC-49 and B72.3. We have studied one patient with I-131 B72.3 human chimeric antibody. As expected the halflife is circulation of the chimeric is longer than that of the murine I-131 B72.3 counterpart.